1. Field of the Invention
The present invention relates to a testing method and a testing system for testing a printed circuit board in a noise analysis manner by injecting a signal simulating noise thereinto.
2. Description of the Related Art
A required operation speed in an electronic apparatus increases for handling a large amount of information, and, along therewith, EMI noise (electromagnetic interference noise) emitted by the electronic apparatus increases, for which appropriate countermeasure is required. Since EMI noise may cause malfunction of a neighbor electronic apparatus, restriction is applied by means of a rule/law worldwide. Unless the restriction is satisfied, import to or sales in the relevant country are not allowed. Accordingly, when an electronic apparatus which is to be sold in a country does not satisfy the restriction of the country, the sales should be stopped or canceled, whereby a significant loss may occur in a manufacture. Notwithstanding, EMI noise countermeasure may have not necessarily been strictly taken in a series of procedure concerning development of electronic apparatuses.
Along with increase in an operation speed, complicatedness, and a circuit density in an electronic circuit, the number of places generating noise increases, and thus, determination thereof may become difficult. Especially, noise generated by an electronic circuit due to increase in its operation speed may become a serious problem.
However, actually, since many possible noise sources exist in a printed circuit board, determination of a target noise generating source therefrom may be very difficult.
When only a single noise generating source is present, whether or not a serious problem occurs, or a cause of the problem if any, may be easily determined from a noise distribution obtained by a noise visualization measurement apparatus or such.
Japanese Patent No. 3263672 discloses a noise injector and a noise injecting method for example. In this method, noise (in a common mode or a normal mode) is added to commercial power supply in a condition in which power is turned on in a to-be-measured apparatus, and respective noises (in a common mode or a normal mode) are injected to a power supply line and a ground line of the to-be-measured apparatus. However, in this method, since the noise is injected to the power supply line of the to-be-measured apparatus, a target noise source may not be properly determined.
Further, since various frequency bands of noises may be generated from a device (IC), impedance of a part into which noise is injected should be considered upon noise injection depending on a frequency band of the noise to inject.
Further, this method relates to injection of signal simulating external noise.
Thus, the purpose is different from a purpose of present invention that an influence of EMI noise generated by a device included in a printed circuit board is measured.
Further, in this method, a device operation is necessary to measure. However a purpose of the present invention is to measure how a noise signal spreads from a power supply terminal or such, and thus, to measure an influence on a substrate itself. Accordingly, the to-be-tested substrate should not necessarily operate properly for the testing purpose.
Further, Japanese Laid-open Patent Application No. 2002-318253 for example discloses a noise visualization system and a display method therefore. In this art, a high frequency signal simulating noise is injected to a to-be-tested apparatus via a wire harness from an injection probe. However, in this document, how to treat standing waves generated in a cable is not addressed. In this method, radiation from the cable may be included in a measurement result of the noise visualization apparatus and thus, a measurement result only from the to-be-tested substrate may not be accurately obtained.
As a result, the measurement result may vary depending on an actual positional relationship between the cable and the to-be-tested substrate. In order to solve this problem, a measurement method is required in which radiation from a cable is prevented from interfering the to-be-tested printed circuit board.